In data transmission systems, data is often transmitted to a remote location by transmitting frequency-shift keyed (FSK) signals over a telephone line. An FSK signal received at the remote location is demodulated to recover the original data signal. To this end, a number of digital FSK demodulators have been proposed. The prior known FSK demodulators are designed to process analog line signals. Thus, if such FSK demodulators were to be used in a terminal with digitized line signals, for example, a .mu.-1aw PCM signal, the individual line signals to be demodulated would require digital-to-analog conversion before demodulation. Additionally, digital multipliers would be required which are complex and, therefore, undesirable.